Howdy,
I did some research on the w6po amp. I assumed it was a 1500 W output amp
not a 1KW input amp. Big difference.
At 1 KW input and dissipation on the order of 500-600 watts the 4C440 blower
should be sufficient.
Previous high power design experience with 8877 amps has taught me that one
should only use the "minimum" airflow specs if you are willing to incur the
expense of replacing 8877s....multiple times! The amp is usually not as
efficient as you think.
73, Bob, W5AH
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of Mike McCarthy, W1NR
Sent: Thursday, April 05, 2007 10:48 AM
To: Bob Alexander
Cc: Hugh Duff; amps@contesting.com
Subject: Re: [Amps] 8877 blower requirement ?
Bob Alexander wrote:
> Hugh,
> The 4C440 only has 60 CFM at 0 static pressure... an 8877 needs around 40
> cfm at .6" SP. and the 4c440 does not meet this spec.
> I do not know the specs on the 2C610 but it is probably around 70CFM at
.6
> SP so it would be
> the best choice of the two....even though noisier.
> 73, Bob W5AH
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
> Behalf Of Hugh Duff
> Sent: Thursday, April 05, 2007 6:51 AM
> To: amps@contesting.com
> Subject: [Amps] 8877 blower requirement ?
>
>
> I have just about finished building a W6PO style 8877 amplifier for 2
> metres and I now need to install a blower. I have a 2C610 (140 CFM) and
> a 4C440 (60 CFM) and I'm wondering which one, if either, would be
> suitable. The latter would be desireable for lower noise but I want to
> make sure the tube is sufficiently cooled without overdoing it. The
> Eimac datasheet that I have simply states "Cooling: Forced Air" with no
> CFM airflow specified.
>
> I've seen rogue statements to the effect of "the bigger (more CFM) the
> better" but according to the Econco "Tube Maintenance" document, too
> much cooling may affect the electron emission of the filament.
>
> So I'm curious to know what the optimum CFM requirement is to
> sufficiently cool a single 3CX1500a7.
>
>
> 73 de Hugh VA3TO
> www.va3to.com
>
>
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>
The 3CX1500A7/8877 lists the minimum airflow and static pressure
required for adequate cooling at various power levels and altitudes.
For example at the maximum 1500W dissipation level 38 CFM at .60 inches
of pressure is required. At 10,000 ft. the requirements are 55.5 CFM at
.88 inches of pressure. However, an 8877 at 1000W dissipation (more in
line with Amateur legal limits) needs 20.3 CFM at .23 inches of pressure
when operated at sea level.
The manufacturer data sheet for the blower should have the CFM/pressure
curves to determine the correct requirements. A 4C440 blower drops to
23 CFM at .5 inches pressure, so it is not adequate to cool an 8877 at
full 1500W dissipation at sea level. But, the 4C440 will deliver 49 CFM
at .3 inches, so it appears to be more than adequate for 1500W OUTPUT
applications.
See the full data sheet at http://www.g8wrb.org/triodes.php
The blower specs can be found on http://www.grainger.com
Mike, W1NR
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